The invention relates to knives and particularly to safety knives of the kind where a part of a blade projects from a handle and there is provided a guard to shield the point and/or cutting edge of the blade so as to prevent or minimise the risk of accidental injury to a user of the knife.
In existing knives of this type, however, the guard for the blade is usually fixed and spaced from the blade so that the cutting edge of the blade is exposed. The object is to allow the exposed cutting edge to be applied to the material to be cut, while the fixed guard is intended to reduce the risk of a part of a person""s body, or other surface or object, accidentally coming into contact with the exposed cutting edge when the knife is handled. Although such arrangements may reduce the risk of accidental injury or damage there is still some possibility of such injury or damage occurring since the exposed blade is still accessible, even though access to it is limited to a certain extent by the guard.
The present invention sets out to provide an improved form of safety knife where these disadvantages may be overcome.
According to the invention there is provided a safety knife comprising a handle, a blade mounted on the handle so that at least a portion of the blade projects from the handle, and at least one guard which is mounted on the handle for movement between an extended position where it overlies at least a part of the cutting edge of the blade, and a retracted position wherein said part of the cutting edge is exposed, resilient biasing means being provided to bias the guard towards the extended position.
Thus, during normal handling of the knife, the protective guard may be sufficient to prevent or reduce the risk of the projecting part of the blade accidentally cutting a person or damaging surfaces or materials, provided that the guard is not engaged with a force sufficient to overcome the resilient biasing means. At the same time, the more positive force which is likely to be applied in deliberate use of the knife for cutting will overcome the resilient bias acting on the guard, causing the guard to be displaced so that the cutting edge of the blade contacts the material being cut. The guard may thus be of any desired size or shape and, since it is retractable it may completely overlie the whole of the projecting part of the blade so that none of the blade is exposed when the knife is not in use.
Preferably the guard is at least partly retractable into a recess in the handle as it moves from the extended position towards the retracted position.
Said resilient bias means may comprise a spring, such as a helical compression spring, mounted on the handle and engaging a part movable with the guard.
The guard may move from its extended position to its retracted position with translatory linear movement. Alternatively, the guard may move from its extended position to its retracted position by angular pivotal movement.
As previously mentioned, the guard, when in the extended position, may overlie substantially the whole of at least one side face of the portion of the blade which projects from the handle.
There may be provided on the handle adjustable stop means movable between a locking position, in which it prevents the guard from moving from its extended position, and a release position in which it permits movement of the guard from its extended position to its retracted position. The stop means may comprise an element which is movable, by operation of a manipulating member, from a locking position in which it obstructs movement of a part movable with the guard, to a release position in which it does not obstruct movement of said part. Said movable element may be rotatable from its locking position to its release position. Said manipulating member may comprise an operating lever connected to the rotatable element so that angular movement of the lever effects rotation of the rotatable element between its locking and releasing positions.
In one embodiment, the rotatable element may comprise a disc having a peripheral edge, a portion of which lies in the path of movement of a part movable with the guard when the disc is in its locking position, said peripheral edge being formed with a recess which lies in the path of movement of said part movable with the guard when the disc is rotated to its release position, so that said part may enter the recess and permit movement of the guard from its extended position to its retracted position.
Alternatively or additionally, the rotatable element may be formed with an abutment which lies in the path of movement of a part movable with the guard when the element is in its locking position and is moved out of said path of movement when the element is rotated to its release position.
In any of the above arrangements said movable element is preferably biased into its locking position by spring means.
In the case where the movable element is rotatable, said operating lever may be directly connected to the rotatable element. Alternatively, the operating lever may be mounted on the handle for pivotal movement separately from the rotatable element, and may have a part which is engageable with the rotatable element in a manner to rotate the element to its release position upon pivotal movement of the lever.
In any of the arrangements previously described, there are preferably provided two of said guards mounted on the handle on opposite sides of the portion of the blade which projects from the handle. In this case the two guards are preferably both controlled by a single movable element and manipulating member. The two guards may be connected together so as to move in unison.
Means may be provided for adjusting the position of each guard independently of the other. For example, means may be provided for locking one guard in a retracted position while the other guard remains movable from its extended position to its retracted position against the action of said resilient balancing means.
In any of the above arrangements there may be further mounted on the handle manually adjustable stop means for adjusting the distance which the guard may move from its extended position towards its retracted position. For example, the adjustable stop means may comprise a movable stop element mounted on the handle and formed with a plurality of recesses of different depths which may be selectively moved into the path of movement of a part movable with the guard, whereby the extent of permitted movement of the guard is determined by the depth of the recess which is brought into said path of movement. The part movable with the guard may comprise a pin extending laterally from the guard. In this case, the laterally extending pin may pass through a slot in the handle, so as to project to the exterior of the handle, said movable stop element being mounted on the exterior of the handle.
The movable stop element may be in the form of a rotatable disc, said recesses of different depths being spaced apart around the periphery of the disc.